LU82114A1 - IMPROVEMENTS IN CONTINUOUS COOLING PROCESSES FOR LOW-CARBON STEEL MACHINE WIRE - Google Patents

Description

* »\ * #L C 2012/8001. BL-2821

PATENT

METALLURGICAL RESEARCH CENTER -CENTRUM VOOR RESEARCH IN DE METALLURGIE,

Non-profit association - vereniging zonder winstoogmerk in BRUXELLES, (Belgium).

Improvements to the continuous cooling processes of low carbon steel wire rod.

The present invention relates to perfec-

NOT

operations with continuous cooling of low carbon steel wire rod (C 0.15%).

At the exit of the wire rolling mill, the wire rod is subjected to a controlled cooling operation, the characteristics of which depend on the final properties which one wishes to impart to the wire.

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Taking into account the composition of the wire and the final properties that one seeks to give it, the duration, the number, the nature and the intensity of the different phases of the complete cooling process can vary in significant proportions.

; Another aspect of the problem is constituted by the importance of the installations making it possible to carry out the requested cooling, and in particular their bulk in the longitudinal direction, which can have a considerable impact on the investments necessary to carry them out.

It follows that an improvement in any one of the phases of a wire cooling process can have an influence both on the quality of the wire, on the duration of the time necessary to cool the wire completely, on the size of the corresponding installations and consequently, on their cost both of operation and of first establishment.

There are currently numerous methods for subjecting a wire rod at its exit from the rolling mill to a well-defined cooling sequence, most often specific to the quality of wire sought.

In the case of extra-mild steel wires, one seeks essentially a breaking load, an elastic limit and an E / R ratio as low as possible. It is therefore important that, in the final product, the ferritic grain is coarse- * sier and the amount of C in oversatuation in the minimum ferrite.

According to a known method, at the outlet of the last rolling stand, a low carbon steel wire rod is subjected to cooling by spraying water, to a temperature between 850 ° C and 800 ° C, then deposited in non-contiguous turns on a horizontal conveyor, where it is still subjected to cooling by calm air then blown up to a temperature this 1 '! order of 200 ° C at 300 ° C and finally, at this temperature, the wire is; yyf / i /

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"3.- put in reels, for shipment. It is immediately seen that according to this process, a relatively intense and rapid cooling phase in the temperature range favorable to precipitation, follows a phase of maintaining at high temperature, for a relatively long time and that consequently it does not little carbide precipitation occurred when the wire reached winding temperature. Such a procedure does not seem to specifically lead to wires with a particularly soft shade, since there is no provision for an aging phase consecutive to such cooling.

The present invention relates to a process for cooling wire rod substantially of the kind described above, but which does not have the drawback indicated above and has, compared to these, the advantage of arriving very easily with a mild steel wire (C 4 0.4%) and even extra soft (C 4 0.15%). It is therefore the essence of the process of the invention, to arrive at a wire whose E / R ratio and the breaking load are particularly low. Furthermore, it is also possible, according to the invention, to carry out this cooling on a shorter and therefore less expensive installation.

It has in fact been found, unexpectedly, that the fact of passing very rapidly from the zone where the allotropic transformation was carried out at least 80%, to that of the start of aging, does not appreciably modify the properties of the metal; a significant saving of time and therefore of installation length was possible, a gain which has proved to be particularly significant in the process of the present invention.

The process which is the subject of the present invention is essentially characterized in that, at the outlet of the rolling mill, the wire rod is brought to a temperature of between 900 ° C. and 780 ° C. and deposited in the form of non-contiguous turns, on a conveyor on which it moves, in that it cools in turns on the conveyor, by adjusting the cooling rate A /. 7 I. * yf I 4.- at a value low enough for the ferritic grain to have the desired size, preferably at least LSTK S, when the allotropic transformation has been carried out to the extent of at least 80% and preferably greater than 95% , in that thereafter and still on a conveyor, the wire is subjected to rapid cooling, to a temperature between 350 ° C and 5bC ° C, and preferably between 500 ° C and 560 ° C, then at the outlet from this phase this rapid cooling, to a second phase of slow cooling î in coils.

i! This rapid cooling is advantageously obtained by immersing the wire in an aqueous bath, preferably at times. 'boiling temperature and which may contain surfactants.

The minimum cooling speed to be observed | so that the saving of time, and therefore that of the installation length, are large enough to be considered advantageous, depends on the diameter of the wire considered. For example for: a diameter of 5.5 mm, a speed of at least 10 ° C / second is desirable, while for a wire of 12 mm in diameter, a speed of at least 3 ° C / second is desirable desirable.

It goes without saying that the final characteristics obtained in the wire mainly depend on the duration of the slow cooling at high temperature, before the rapid cooling. The longer this duration, the lower the E / R ratio obtained, as well as the value of R and E. For a given length of installation, the mechanical characteristics therefore depend on the rate of cooling of the wire on said conveyor.

Thanks to this process, we quickly obtain | a soft and even extra-soft yarn of very good quality, by means of an installation the length of which can be much less than that normal of the known process mentioned above.

'Compared with other methods, the method of the invention therefore makes it possible: desired and the major part of the allotropic transformation, - to reduce, in a very important way, the time of passage from the high temperature zone to that of overaging, which has the advantages of keeping a maximum. of carbon in supersaturation in the ferrite and to reduce the length of the installation, - an aging phase of particularly long duration, while still significantly reducing the length of the installation, since this last phase is carried out after the * reel.

The diagrams below, given by way of nonlimiting example, make it possible to appreciate the advantages of the process of the invention.

In the diagram of FIG. 1, there is shown, according to a known process, the time evolution of the temperature of a steel wire rod, 5.5 mm in diameter and whose composition is: 0.05% C and 0.3% Mn, 0.0 ^ 8% K. This wire, deposited at the temperature of 850 ° C on a conveyor moving at 0.3 m / sec. and cooled in still air and wound at around 250 ° C after 150 seconds of cooling according to the said development, has a breaking strength of 370 N / mm; the length of the installation is about 50 m.

In FIG. 2, and in accordance with the process of the invention, the same wire is deposited at 850 ° C., under the same conditions of conveyor speed, but subjected to cooling at 2.5 ° C./sec., Up to to 750 “C, then to rapid cooling to 500 ° C in about 16 seconds at the speed of 16 'C / sec and finally to slow cooling (this overaging) in coil, to room temperature. Operation card that can be performed on an installation whose length is approximately 1? m, the interest of this way of proceeding is therefore obvious. Let us note /// that according to this process, the results obtained for the ni subjected to it // are: E / R = 0.7 and R = 330 N / mm-.

Claims (6)

1. A method of cooling a low carbon steel wire (C * 0.15%), characterized in that at the exit of the rolling mill, the wire rod is brought to a temperature between 900 ° C and 780 ° C and deposited in the form of non-contiguous turns, on a conveyor on which it moves, in that the wire is cooled - in turns on the conveyor by adjusting the cooling rate to a value sufficiently low so that the ferritic grain has the desired size when the allotropic transformation has been carried out to the extent of at least 80%, and preferably su | below 95%, and in that thereafter and still on the conveyor, the wire is subjected to rapid cooling down to a temperature between 350 ° C and 560 ° C, and preferably between 1500 ° C and 560 ° C, and then at the end of this rapid cooling phase, to a second cooling phase, carried out in coils; 2. Method according to claim 1, characterized in that the rapid cooling rate is chosen sufficient for oue the major part at least of the carbon remained in supersaturation! I at the end of the allotropic transformation is still at the beginning | [I of the aging phase. ; | 3. Method according to either of the claims 1 and 2, characterized in that the speed of the first cooling: I *; "Slowly on the conveyor is such that the grain size reaches at least ASTM 9. i j 4. Process according to either of the claims; 1 to 3, characterized in that rapid cooling is; 1 obtained by immersing the wire in an aqueous bath, preferably at boiling temperature. * / 7. - 5. Method according to claim 6, characterized in that the rapid cooling rate is at least 10 ° C / second for a diameter of 5.5 mm and at least 3 ° C / second for a diameter of 12 mm. 6. Method as described above. // the